Research On The Detonation Synthesis Of Carbon-Encapsulated Nano-Permalloys

In the wake of developments in science and technology,there is an increasing demand for material properties.As an important soft magnetic material,permalloy has a wide range of applications in many fields.However,nano-permalloy cannot be stable in the air,which limits the range of applications of this material.Scientists suggest that carbon coating can solve this problem,carbon-encapsulated alloy nanomaterials combine the advantages of carbon-encapsulated metal nanomaterials and alloy materials,which have great performance advantages over traditional materials.Many methods have been proposed for the synthesis of core-shell nanomaterials.Among them,the most typical methods are arc discharge method(Arc),chemical vapor deposition(CVD),pyrolysis,etc.Great achievements have been made by these methods in the synthesis of carbon-encapsulated nanomaterials,however,these methods have problems such as high energy consumption,expensive instrument,inability to continuously synthesize,difficult to strip by-products,and low economics,which do not have the basis of industrial production in general.As a synthetic method with industrialization basis,detonation has been widely used in the synthesis of nanomaterials which has the advantages of fast reaction speed,low energy consumption,simple process parameters,large-scale continuous production,and good economy.The detonation synthesis of nano-diamonds has been successfully industrialized.In this paper,the carbon-encapsulated permalloy nanomaterials were prepared by explosive detonation method and gas-phase detonation method,the experimental analysis,performance testing and theoretical calculation were respectively carried out.The microstructure and phase composition of the material was characterized and research by modern detection methods:X-ray diffractometer(XRD),transmission electron microscopy(TEM)with EDS spectrum,Raman and other modern analytical methods.The performance of detonation products was tested and studied by means of material performance testing methods such as vibrating sample magnetometer(VSM)and vector grid analyzer.Detonation parameters of the explosive detonation and gas-phase detonation were calculated by numerical simulation respectively,and high-speed photography verified the accuracy of the calculation.The synthetic mechanism of detonation synthesis of carbon-encapsulated nanoparticles was discussed in depth combined with the alloy phase diagram.The following results are obtained:1)The inexpensive and readily available nitrates were used as metal-core donors,ethanol and naphthalene were used as carbon source donors,respectively.The nanoparticles with the tightly packed core-shell structure were successfully synthesized by a reasonable adjustment of the precursor components in a special detonation pressure vessel.Research on detonation products shows that there was occasional agglomeration in explosive detonation products due to collision of Brownian motion;the diameter of core of the product was increases with the increase of atomic ratio of nickel;the thickness of the carbon layer was proportional to the carbon content of the precursor.The product showed good superparamagnetism and excellent electromagnetic wave absorption effect at room temperature which was also easily modified to be a good absorbing coating material.2)The BKW condensed state equation combined with the Gibbs minimum free energy principle and the solid equation was also coupled for the explosive detonation.According to the ZND model of detonation,the numerical calculation of the detonation parameters of synthesis carbon-encapsulated nanomaterials was realized.According to the calculation results of the program,the mechanism of detonation synthesis of carbon-encapsulated nanomaterials was discussed based on the combination of carbon metal binary alloy phase diagrams.The coating layer was composed of graphite and amorphous carbon,wherein part of the graphite was derived from detonation of activated carbon clusters under the catalysis of iron and nickel,and another portion was derived from highly graphitized carbon precipitated inside the metal during cooling and depressurization;the non-spherical carbon-encapsulated nano-alloy particles were derived from the collision polymerization of the particles after the alloy enters the solid phase,which had not enough time to grow into equiaxed grains.3)The metalorganic materials which are easy to vaporize are respectively made of carbon-encapsulated nano permalloy,carbon-encapsulated nano hyper permalloy and carbon-encapsulated nano copper-iron alloy by using gas-oxygen explosion source and acetylene oxygen explosion source in gas detonation tube,respectively.The appearances of detonation products were similar which had few local agglomerations with core-shell structures and ultrafine nanoparticles with a uniform particle size distribution of about 10 nm.The copper-iron alloy showed a completed graphite coating at a ratio of the proportion of the precursor metal to the iron atom of 30%.The exploratory experiment on the carbon-encapsulated multi-alloy was carried out in a 5%Mo-doped permalloy product.It was found that Mo element exists in the form of stable carbide which was not conducive to improving soft magnetic performance,and Cu doping should be used when synthesizing carbon-encapsulated super-permalloy by detonation.4)Aimmed at the special problem of parameter calculation of gas-phase detonation synthesis,an ideal gas mixed with solid particle equation of state was proposed.Based on the C-J detonation theory,the influences of initial pressure and initial temperature of the gas phase detonation were corrected.According to the detonation speed obtained by high-speed photography,the theoretical calculation had a good agreement between practice.The calculation of the detonation parameters for the experimental conditions in the paper indicated that the temperature of the gas phase detonation synthesis will be above the boiling point of the iron(2750?)meanwhile below the carbon boiling point(4827?).Compared with the detonation synthesis of solid-phase explosives,since the metal was in a gaseous state and the space content of metal was low during gas detonation synthesis,which was beneficial to the formation of ultrafine nanoparticles.